Problem: If $5a + 9b = -5$ and $9x + 3y + 8z = -1$, what is $10a - 16z - 6y - 18x + 18b$ ?
Solution: $= 10a + 18b - 18x - 6y - 16z$ $= (2) \cdot (5a + 9b) + (-2) \cdot (9x + 3y + 8z)$ $= (2) \cdot (-5) + (-2) \cdot (-1)$ $= -10 + 2$ $= -8$